Biology and Physical Factors #1: Basics

Certain features are common to many life forms. Why? That is the theme of Raghuveer Parthasarathy’s So Simple a Beginning. There are multiple angles from which one can approach that question, and this book looks at it “through the lens of physics”.

 

In the book, his focus is on 4 principles from physics that recur often in biological organisms: (1) self-assembly; (2) regulatory circuits; (3) predictable randomness; and (4) scaling.

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Before diving into all that, he first explains the basic building blocks of life. DNA, as we know, has 2 strands. To read it, we need to first separate the strands. Which leads to the question: Does DNA melt?

 

This may sound like a weird question, so Parthasarathy explains its significance. Ice melts if you raise the temperature above 0° C (a precise temperature). But not everything is like that. Honey doesn’t suddenly change state upon heating - it just becomes progressively less viscous. Now for the relevance to DNA splitting. If DNA is like water (with a sharp phase change temperature), then raising the temperature to that point will lead to “complete separation” (top half of the pic). But if DNA is like honey (without a sharp phase change temperature), then we’d have “some unseparated DNA” (bottom half): 

You might think you could continue to heat it further until they fully separated. But the problem is that the higher temperature could damage the DNA.

 

It turns out DNA does melt, making DNA analysis possible (The separated strands can be analyzed far more easily than the double-helix).

 

One view of DNA is that it is a code, a sequence of instructions to build proteins and the entire organism. While that is certainly true, Parthasarathy says:

“DNA is more than a code or an abstraction, it is a tangible, physical object.”

Going back to the theme (and perspective) of this book:

“We can’t understand DNA without understanding its physical properties. Shape, structure and mechanics are inextricably tied to biological function.”

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Take another basic building block of life: proteins. Proteins can fold in different ways; and if they fold the wrong way, they can cause serious problems. How?

“In the “normal” form, the protein performs its usual functions. In the “misfolded” form, it does not.”

 

Biology, we see again, is influenced by physical factors.